Ensures ThinkingSphinx preloads the all the indices

Otherwise concurrent threads (e.g. sidekiq, puma) can deadlock while
racing to obtain access to the mutex block at
https://github.com/pat/thinking-sphinx/blob/v3.4.2/lib/thinking_sphinx/configuration.rb#L78.

This bug was fixed in ThinkingSphinx v4.3.0+.

See
- pat/thinking-sphinx#1051
- pat/thinking-sphinx#1132

config/initializers/sphinx.rb

@@ -1,3 +1,8 @@
 SPHINX_DELTA_INTERVAL = 90.minutes
 
 ThinkingSphinx::Callbacks.suspend!
+
+# Prevents concurrent threads (e.g. sidekiq, puma) to deadlock while racing to obtain access to the mutex block at https://github.com/pat/thinking-sphinx/blob/v3.4.2/lib/thinking_sphinx/configuration.rb#L78
+# This is a ThinkingSphinx's known bug, fixed in v4.3.0+ - see: https://github.com/pat/thinking-sphinx/commit/814beb0aa3d9dd1227c0f41d630888a738f7c0d6
+# See also https://github.com/pat/thinking-sphinx/issues/1051 and https://github.com/pat/thinking-sphinx/issues/1132
+ThinkingSphinx::Configuration.instance.preload_indices if Rails.env.development?